Sensorless measurement of positioning travel, especially on an electromotively operated parking brake

ABSTRACT

The invention relates to a method for establishing the position of an actuating unit which is operated by an electric motor, in which a motor speed is determined from a motor model, the speed is integrated over a period of time and the position of the actuating unit is determined by multiplying the result of the integration by a proportionality factor. The motor model takes account of afterrunning of the electric motor at the instant of switch-off. The invention also relates to actuating units, brakes, pumps and transmissions for which the method can be used.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/EP2005/013486 filed Dec. 15, 2005, the disclosures of which areincorporated herein by reference, and which claimed priority to GermanPatent Application No. 10 2004 061 917.4 filed Dec. 22, 2004, thedisclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention relates to a method for establishing the position of anactuating unit which is operated by an electric motor. The inventionalso relates to brakes, pumps and transmissions in which actuating unitsof this kind are used.

In the case of, for example, an electronic parking brake (EPB) which isoperated by an actuating unit the motor speed is as a rule currentlymeasured by sensor technology (for instance by means of a Hall sensor).The number of detected revolutions (or of pulses delivered by the Hallsensor) multiplied by a motor constant gives the travel completed by theactuating unit. However high costs are incurred by fitting a Hall oranother sensor.

Approaches for establishing a motor speed without a sensor, e.g. fromthe number of commutation changes, are already known. However these havethe disadvantage of being susceptible to faults. The patent DE 197 29238 C1, and corresponding U.S. Pat. No. 6,144,179, both of which areincorporated by reference herein, describes, for example, a method forestablishing the speed of mechanically commutated D.C. motors in whichthe speed is established from a motor state model in parallel with thedetection of the waviness (current ripple) of the motor current. Thespeed is firstly established from the motor state model, which is basedon the electromechanical motor equations, after which a reliable settime range is predetermined for the following commutating process. If nowaviness is detected within this set time range on account of a fault,the probable speed and the probable commutating instant derived from thelatter are assumed.

The object of the present invention is to precisely establish the travelof an actuating unit without using additional sensor technology. Afurther object of the present invention is to enable the travel of theactuating unit to be quickly determined continuously or at short timeintervals.

BRIEF SUMMARY OF THE INVENTION

The above-mentioned objects are achieved by a method according to theinvention for establishing a position of an actuating unit which isoperated by an electric motor, comprising the steps of determining amotor speed from a motor model, integrating the motor speed over aperiod of time and determining the position of the actuating unit bymultiplying the result of the integration by a proportionality factor,wherein the motor model takes account of afterrunning of the electricmotor. By means of integration the travel which is completed by theactuating unit can be calculated from the motor speed, which ismultiplied by a proportionality factor.

One concept of the method presented in the invention is a distance modelto which measured operating data with which a motor speed is calculatedfrom a motor model are preferably in any case delivered. Measuredoperating data are the operating voltage U_(q) applied to the motorterminals and the current I_(mess) measured in the lines. Furtheroperating data may also be delivered to the motor model.

In one embodiment the motor model takes account of a loading torqueacting on the electric motor at the instant of switch-off. In oneembodiment the motor model takes account of damping proportional to thespeed in addition or alternatively to this.

In a further embodiment the speed-proportional damping is included inthe motor model as a damping torque, wherein the damping torque, equalto a damping constant, is multiplied by an angular speed of the electricmotor. In one development of the invention the damping constant is equalto a no-load friction torque divided by a no-load angular speed of themotor. However other approaches for establishing the speed-proportionaldamping are also conceivable.

In a further embodiment, which can be combined with the aboveembodiments, the motor model additionally takes account of a loadingtorque in that the torque is preferably determined from a measured motorcurrent, with an efficiency factor of an electrical part of the electricmotor being taken into account.

The method according to the invention can be carried out in accordancewith (external or internal) trigger signals. Thus the method canadditionally comprise the step of connecting a trigger signal as thefirst step, wherein the step of determining the motor speed is onlyexecuted when the trigger signal is connected.

The method according to the invention can also additionally comprise thestep of disconnecting the trigger signal as the last step, wherein theapplied load torque is determined when the trigger signal isdisconnected. The load torque can be delivered to the model (constantlyor only at certain instants), e.g. as long as the speed calculated bythe model is greater than zero and the applied load torque assumes thevalue zero when the calculated speed is zero.

According to one development, the induced voltage is delivered as thesupply voltage to the model when the trigger signal is disconnected. Ina further embodiment an integrator for calculating speed and travel isreset at the beginning of the calculation at each rising edge of thetrigger signal.

The method according to the invention can additionally comprise the stepof converting the speed into revolutions per second.

A computer program product according to the invention for establishingthe position of an actuating unit operated by an electric motorcomprises program codes for executing the steps of determining a motorspeed from a motor model and determining the travel completed by theactuating unit by integrating the motor speed over a period of time andmultiplying it by a proportionality factor, wherein the motor modeltakes account of afterrunning of the electric motor.

The method according to the invention can generally be used in anactuating unit and specifically, for example, in an electromechanicalbrake (EMB), an electric parking brake (EPB), a hydraulic parking brake(HPB), a pump unit of an anti-lock braking system (ABS) and atransmission.

An actuating device according to the invention comprises an electricmotor and an actuating unit, which is operated by the electric motor,with a memory unit for a motor model and with a processor, wherein, inorder to establish the position of the actuating unit operated by anelectric motor, the memory unit comprises program codes for executingthe steps of determining a motor speed from a motor model anddetermining a travel completed by the actuating unit by integrating themotor speed over a period of time and multiplying it by aproportionality factor, and wherein the motor model takes account ofafterrunning of the electric motor.

A brake according to the invention comprises an actuating deviceaccording to the invention as described above, wherein the actuatingdevice actuates the brake.

A pump device according to the invention comprises an actuating deviceaccording to the invention as described above, wherein the actuatingdevice actuates the pump device.

A transmission according to the invention comprises an actuating deviceaccording to the invention as described above, wherein the actuatingdevice actuates the transmission.

Other advantages of this invention will become apparent to those skilledin the art from the following detailed description of the preferredembodiments, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an equivalent circuit diagram for a D.C. motor with a loadconnected to the D.C. motor,

FIG. 2 shows an equivalent circuit diagram in terms of controlengineering,

FIG. 3 shows an equivalent circuit diagram in terms of controlengineering with speed-proportional damping,

FIG. 4 shows an equivalent circuit diagram in terms of controlengineering with the speed-proportional damping and estimation of theload torque,

FIG. 5 shows an equivalent circuit diagram in terms of controlengineering with the speed-proportional damping, the estimation of theload torque and a trigger signal,

FIG. 6 shows an equivalent circuit diagram in terms of controlengineering with the speed-proportional damping, the estimation of theload torque and the trigger signal, wherein the load torque is estimatedat the instant when the motor is switched off,

FIG. 7 shows an equivalent circuit diagram in terms of controlengineering with the speed-proportional damping, the estimation of theload torque and the trigger signal, wherein the load torque is estimatedat the instant when the motor is switched off and account is taken ofthe voltage conditions at the motor when switching off takes place,

FIG. 8 shows an equivalent circuit diagram in terms of controlengineering with the speed-proportional damping, the estimation of theload torque and the trigger signal, wherein the load torque is estimatedat the instant when the motor is switched off, account is taken of thevoltage conditions at the motor when switching off takes place and anintegrator is provided for calculating speed and travel,

FIG. 9 is a schematic representation of an actuating device with anelectric motor, an actuating unit, a processor and a memory unit.

DETAILED DESCRIPTION OF THE INVENTION

In order to establish a motor model for a D.C. motor which is excited bya permanent magnet, the equivalent circuit diagram of the separatelyexcited D.C. motor can generally be taken as a starting point.

The following variables are used in the following:

U_(q) applied operating voltage (terminal voltage)

U_(o) induced voltage in the motor on account of the rotational movement

R_(i) armature resistance

L_(a) armature coil inductance

I_(q) armature current

I_(mess) measured motor current

ψ_(d) magnetic flux

K_(m) motor constant (indicated by the manufacturer, unit: Nm/A)

s Laplace variable

ω angular speed of the motor (angular frequency)

J moment of inertia of the load

M_(el) electrically generated driving torque

M_(L) load torque on the motor shaft

M_(T) acceleration torque

M_(d) damping torque

c proportionality constant

T_(a) armature time constant

M_(fr∞) no-load friction torque (unit: Nm)

I_(∞) no-load current (unit: A)

Ω_(∞) no-load angular speed (unit: rad/s)

b damping constant (unit: Nm sec/rad

η efficiency factor

A voltage which is induced in an armature of an electric motor isgenerally calculated as:U ₀(s)=c·ψ _(d)·ω(s)  (equation 1.0)

Here s is the Laplace variable by means of which the arisingdifferential equations, as are usual in control engineering, arewritten. The proportionality constant c is designated the machineconstant, which depends, inter alia, on the geometric dimensions of themotor windings.

From this follows, for the voltage cycle in an armature circuit of anelectric motor:U _(q)(s)=I _(q)(s)·(R _(i) +s·L _(a))+U ₀(s)  (equation 1.1)

The armature time constant T_(a) is given by:

$\begin{matrix}{T_{a} = \frac{L_{a}}{R_{i}}} & \left( {{equation}\mspace{14mu} 1.2} \right)\end{matrix}$

The following is obtained by adapting equation 1.1 and using equation1.2:

$\begin{matrix}{{I_{q}(s)} = {\frac{\left( {{U_{q}(s)} - {U_{0}(s)}} \right)}{R_{i}} \cdot \frac{1}{1 + {s \cdot T_{a}}}}} & \left( {{equation}\mspace{14mu} 1.3} \right)\end{matrix}$

From the general motor constant k_(m), given byk _(m) =c·ψ _(d)  (equation 1.4),which can be obtained from a motor data sheet also supplied by the motormanufacturer, the torque which can be electrically generated, M_(el),can be calculated:M _(el) =k _(m) ·I _(q)(s)  (equation 1.5)

The generated electrical driving torque M_(el) is in equilibrium withthe load torque M_(L) and the torque M_(T) which is necessary for theacceleration or deceleration of the inertias. Using the Laplacetransformation, the torque M_(T) which is necessary for acceleration ordeceleration is calculated as:M _(T)(s)=J·s·ω(s)  (equation 1.6)

Expressed as torque equilibrium:M _(T)(s)=M _(el)(s)−M _(L)(s)  (equation 1.7)

The equations 1.1 to 1.7 represent the basic model for the d.c. motor.The motor model reproduces the system behaviour both dynamically andstatically. The basic model is extended as follows in order to obtain ausable model for estimating travel.

The motor model of the d.c. motor is firstly extended byspeed-proportional damping. The afterrunning or running-down behaviourof the motor upon being switched off can additionally be taken intoaccount.

The friction torque M_(fr∞) occurring at no-load speed is caused bybearings and brush friction as well as by mechanical and electricallosses in the air gap or iron of the rotor. The bearings and brushfriction can be modelled as Coulomb friction, the losses in the air gapand in the iron as viscous friction. The friction torque is the sum ofboth components. It is obtained with the motor constant from the no-loadcurrent. In order to obtain a linear model, the entire friction isassumed to be proportional to the speed. The associated damping constantis calculated from the data sheet details of the motor manufacturer.

$\begin{matrix}{b = {\frac{M_{{fr}\;\infty}}{\Omega_{\infty}} = \frac{k_{m} \cdot I_{\infty}}{\Omega_{\infty}}}} & \left( {{equation}\mspace{14mu} 1.8} \right)\end{matrix}$

As indicated, this damping is proportional to the speed. For the modelthis means that a further term must be taken into account in the torqueequilibrium (equation 1.7). It follows that:M _(d)(s)=b*ω(s)  (equation 1.9)M _(T)(s)=M _(el)(s)−M _(L)(s)−M _(d)(s)  (equation 1.10)

According to one embodiment, the motor model is additionally extendedsuch that the loading motor torque is taken into account. In thisrespect it is of no significance from what the load motor torqueresults. If, for example, the internal friction of the constructionchanges, the motor current changes in direct proportion to this. It isthus possible, by means of the motor current, to calculate the loadtorque from the motor constant (the motor constant is usually indicatedby the motor manufacturer).

The measured motor current is proportional to the load. In this respectit is of no significance from what the load torque results. If, forexample, the internal friction of the construction changes, the motorcurrent changes in direct proportion to this. If the friction increases,the current increases. If the friction decreases, the current decreases.The same applies to a load change at the driving motor shaft. Howeverthe efficiency factor of the electrical part of the motor must be takeninto account. The efficiency factor can be established by usingmeasurement technology. With these interrelationships it is possible tocalculate the load torque from the motor constant k_(m) by means of themotor current.

In order to obtain a real motor model which is in running order, theterminal voltage U_(q) and the current I_(mess) should only be switchedto the model when the motor is actually also activated in theapplication. Otherwise the real behaviour cannot be calculatederror-free, especially when switching on takes place.

A trigger signal is provided in a further embodiment.

By switching on the motor with the trigger signal, the measured batteryvoltage and the current actually flowing are firstly switched to themodel. As long as the trigger signal is zero, the load torque and theoperating voltage for the motor are zero.

The model must be extended in order to switch off the motorrealistically. Since the motor is still afterrunning at the instant ofswitch-off due to the prevailing inertias of the load, armature, shaftand all further driven components, it is possible to work out a solutionwhich reproduces this “afterrunning behaviour” in the best possiblemanner. As the model calculates the applied load torque by means of theflowing current, information on the instantaneous load is available atthe instant of switch-off. This value is retained in a memory cell andat and/or after the instant of switch-off (trigger signal=0) constantlydelivered to the model as long as the speed ω calculated by themodel >0. When the simulated speed 0 is reached, the load torquecalculated from the load current is processed in the model. As a resultof this measure, the temporarily stored load torque assumes the value 0when the motor is finally at a standstill (ω=0). If a load torque werethen still delivered to the model, this would disturb the torqueequilibrium at the summing point of the model and the model wouldcalculate incorrect initial values with the motor at a standstill. Ifthe motor is switched on (trigger signal=1), the load torque actuallyprevailing at the time is immediately reacquired from the load currentand the model can start error-free.

However with the introduced model extensions the model is still notcompletely accurate in the running-down behaviour when the motor isswitched off under load. As voltage is no longer applied to theconnecting terminals of the motor and the motor terminals are open atthe instant of switch-off (U_(q)=0), the afterturning of the motor isonly caused by the mechanical components. However the induced voltage istaken into account in the model as long as the motor is still turning.Yet this is no longer of significance when the motor terminals are open.In order to correctly reproduce the running-down behaviour, the inducedvoltage can therefore be delivered as the supply voltage U_(q) to themodel at the instant of switch-off. This results in U_(q)−U₀=0. 0 isobtained from this equation for the electrical component of the modeland only the mechanical component of the model is still active.

The d.c. motor is reproduced as a transfer function of the armaturecircuit and a representation of the mechanical differential equation. Byswitching on the motor with the trigger signal, the measured batteryvoltage and the current actually flowing are firstly switched to themodel. As long as the trigger signal is zero, the load torque and theoperating voltage are switched to the model. This is important, forotherwise the model would already calculate a speed and misrepresent theoverall result.

At the moment of switch-on the voltage passes via a selection switch tothe summing point before the armature circuit. At this point the inducedmotor voltage resulting on account of the speed is subtracted from theoperating voltage. The voltage which is thus calculated is the soledriving voltage at the armature circuit. The armature consistsessentially of the inductance and the internal resistance of thearmature coil. Considered in electrical terms, this forms a low-passfilter with the time constant T_(a)=L_(a)/R_(i). This fact is reproducedhere as a transfer function.

While a voltage is applied to the input, the resulting armature currentis obtained at the output. This current, multiplied by the motorconstant k_(m), produces the driving motor torque. The load torque andspeed-proportional damping must be subtracted from this, so that theactually driving motor torque is obtained, taking account of theincurred losses. This driving torque, multiplied by the moment ofinertia of the construction, is then integrated, resulting in the speedin the unit rad/s.

The calculated speed in revolutions per second (U/sec) is obtainedthrough conversion. If this speed is integrated during the on-period ofthe motor, the sum of all the revolutions within this period of time isobtained. Finally, the travel which is completed is obtained bymultiplying this result by the constant k_(m) (e.g. k=0.02mm/revolution).

If the motor is switched off, the operating voltage suddenly becomes 0.However the motor continues to turn. In order to simulate this case, theinduced armature voltage which was calculated last is delivered as theinput voltage to the model at the instant of switch-off. This voltagethen tends with time towards 0, whereby the speed also tends towards 0.However it is also important in this respect for the load torque to bereproduced in this case, as the measured current also suddenly becomes 0when the voltage is switched off. For this purpose the load torque whichwas established last is retained in a memory cell and delivered as theload torque to the model until the speed calculated from the model is 0.These measures enable the running-down of the motor to be realisticallysimulated even under fluctuating load conditions.

All the integrators are set to zero each time the motor is switched onagain, so that no old values of a last activation misrepresent theresult.

Finally, extended by these circumstances, an extended model can beestablished.

The speed ω is integrated during the on-period in order to obtain thespindle position. If the result is multiplied by a factor k, which isobtained from the spindle pitch and the transmission ratio, the travelcompleted is obtained. This travel is equal to the actual spindleposition. In the case of the HPB the factor k is, for example, 0.2 mmper motor shaft revolution. The position x (the spindle travel) istherefore calculated as:x=k*k ₁*∫ω(t)dtwith:

$k_{1} = \frac{1}{2\;\pi}$(conversion from rad/sec to revolutions/sec)k=0.02 (transmission ratio/spindle pitch)

A further advantage of this method lies in the fact that the algorithmcan be calculated in 5 msec intervals. The errors occurring due to theslow sampling time in relation to the rapid armature time constant donot have any appreciable effect on the end result.

FIG. 1 shows an equivalent circuit diagram for a D.C. motor 10 with aload 12 having a moment of inertia J connected to the d.c. motor. Anoperating voltage 24, which is designated by U_(q), is applied to theD.C. motor 10 at the connections 20, 22. The armature current isdesignated by I_(q). In the equivalent circuit diagram the resistance 14represents the armature resistance R_(i) of the D.C. motor and theinductance 16 the armature coil inductance L_(a). The induced voltage 28which is generated in the motor on account of the rotational movement isdesignated by U_(o). Electrical lines 18, 19 in each case connect theelectric motor to the connections 20, 22. The magnetic flux (excitationflux) 36 which is required for the rotational movement is generated by astator coil 30, to which a voltage is applied via the connections 32,34. The excitation flux 36 is alternatively generated by a permanentmagnet.

In the equivalent circuit diagram, in terms of control engineering,which is shown in FIG. 2 the operating voltage 50 (again designated byU_(q) as symbol; corresponds to the reference number 24 in FIG. 1) isapplied. The operating voltage U_(q) and the induced voltage U_(o) areadded in an adder 52. The armature current I_(q) is calculated by meansof the equation 1.3 in the calculation step 54. The generated electricaldriving torque M_(el) is calculated from the armature current I_(q) andthe motor constant k_(m) in the calculation step 56. The accelerationtorque M_(T) which is necessary for acceleration or deceleration iscalculated through addition 58 of the driving torque M_(el) to the loadtorque M_(L). The angular speed ω is calculated through division 62 bythe moment of inertia J and through subsequent division 64 by theLaplace variable s. The induced voltage U_(o) is calculated throughmultiplication 68 by the motor constant k_(m) and delivered in afeedback path to the adder 52.

The equivalent circuit diagram from FIG. 3 corresponds substantially tothe equivalent circuit diagram from FIG. 2, although additionally has acircuit with speed-proportional damping according to the invention. Inan additional step 70, after calculating ω in the calculation step 64, adamping torque M_(d) is calculated from the angular speed ω bymultiplying by a damping constant b and delivered to the adder 58. Theadder 58 therefore converts the equation 1.10.

The equivalent circuit diagram from FIG. 4 corresponds substantially tothe equivalent circuit diagram from FIG. 3, although additionallycomprises a circuit for calculating the load torque M_(L). The loadtorque M_(L) is calculated through multiplication 74 of the measuredmotor current 76 by an efficiency factor η (designated in FIG. 4 by eta)and subsequent multiplication 72 by the motor constant k_(m). This isdelivered to the adder 58.

The equivalent circuit diagram from FIG. 5 corresponds substantially tothe equivalent circuit diagram from FIG. 4, although additionallycomprises a trigger circuit for connecting and disconnecting the controlcircuit. The switches 80, 82 are activated via the trigger signal 78. Ifthe trigger signal 78 is disconnected, the terminal voltage U_(q) andthe measured motor current are set to zero. If the trigger signal 78 isconnected, the terminal voltage U_(q) and the measured motor currentI_(mess) are switched to the model.

The equivalent circuit diagram which is shown in FIG. 6 differs from theequivalent circuit diagram of FIG. 5 in that a circuit for estimatingthe load torque at the instant when the motor is switched off isprovided between the multiplication step 72 and the adder 58. If thetrigger signal 78 is connected, a first switching unit 84 transmits thecurrent value of the load torque M_(L) to a second switching unit 88. Ifthe trigger signal 78 is disconnected, the instantaneous value of theload torque M_(L) at the instant when the trigger signal 78 isdisconnected is stored in a memory cell 90 and delivered further to thesecond switching unit 88. The second switching unit 88 transmits thevalue of the load torque M_(L) to the adder 58 until the simulatedangular speed (o becomes zero. Thus the second switching unit 88 onlytransmits the value of the load torque M_(L) to the adder when the motoris in motion. The trigger signal 78 is connected again when the motor isswitched on, so that the actual value of the load torque enters themodel via the first switching unit 84 and the second switching unit 88via the adder 58.

The voltage conditions at the motor upon switching off are additionallytaken into account in the equivalent circuit diagram which is shown inFIG. 7. In order to correctly reproduce the running-down behaviour ofthe motor, the induced voltage is delivered as the supply voltage U_(q)to the model at the instant of switch-off. If the trigger signal 78 isconnected, a third switching unit 92 delivers the terminal voltage U_(q)to the adder 52. As soon as the trigger signal 78 is disconnected, thethird switching unit 92 delivers the induced voltage U_(o) as theterminal voltage U_(q) to the adder 52. Therefore U_(q)−U_(o)=0. Thusonly the mechanical component of the model is still active.

The equivalent circuit diagram in FIG. 8 corresponds substantially tothe equivalent circuit diagram from FIG. 7, with the angular speedadditionally being converted to revolutions per second throughmultiplication 96 in the block k1. The position of the actuating unit iscalculated via the steps 98 and 100. Here, in order to calculate speedand travel, the integrator 98, 100 is reset at the beginning of thecalculation, so that old results do not give rise to any miscalculation.In one embodiment resetting takes place with each rising edge of thetrigger signal 78. The model advantageously works with short calculationtimes, preferably in the μs or ms range. In one embodiment the modelworks with calculation times of 5 ms. The errors occurring due to theslow sampling time in relation to the rapid armature time constant donot have any appreciable effect on the end result.

The expenditure for converting a program code for a microcontroller islow. Porting to a commercial microcontroller, e.g. Siemens C167, isdirectly possible in integer format.

FIG. 9 is a schematic representation of an actuating device according tothe invention with an electric motor 10, an actuating unit 200, a memoryunit 204 and a processor 202. The electric motor 10 drives the actuatingunit 200. The processor 202 executes the method according to theinvention for establishing the position of the actuating unit 200operated by the electric motor 10. The program codes and the measurementdata are stored in the memory unit 204. The processor communicates withthe electric motor 10. All the data required for establishing theposition of the actuating unit 200 operated by the electric motor 10 arefed to the processor 202.

In accordance with the provisions of the patent statutes, the principleand mode of operation of this invention have been explained andillustrated in its preferred embodiment. However, it must be understoodthat this invention may be practiced otherwise than as specificallyexplained and illustrated without departing from its spirit or scope.

1. Method for establishing a position of an actuating unit which isoperated by an electric motor, comprising the steps: determining a motorspeed from a motor model that takes account of afterrunnning of theelectric motor and includes speed proportional damping of the motor;integrating the motor speed over a period of time; and establishing theposition of the actuating unit by multiplying the result of theintegration by a proportionality factor.
 2. Method for establishing aposition of an actuating unit which is operated by an electric motor,comprising the steps: determining a motor speed from a motor model thattakes account of both a loading torque acting on the electric motor atthe instant of switch-off and afterrunnning of the electric motor;integrating the motor speed over a period of time; and establishing theposition of the actuating unit by multiplying the result of theintegration by a proportionality factor.
 3. Method according to claim 2,wherein the motor model additionally takes account of dampingproportional to the rotational speed.
 4. Method according to claim 3,wherein the speed-proportional damping is included in the motor model asa damping torque that is equal to a damping constant multiplied by anangular speed of the electric motor.
 5. Method according to claim 4,wherein the damping constant is equal to a no-load friction torquedivided by a no-load angular speed of the motor.
 6. Method according toclaim 5, wherein motor torque is determined from a measured motorcurrent, and further wherein an efficiency factor of an electrical partof the electric motor is taken into account.
 7. Method according toclaim 6, wherein the method additionally comprises the step ofconnecting a trigger signal as the first step, and that the step ofdetermining the motor speed is only executed when the trigger signal isconnected.
 8. Method according to claim 2, wherein the methodadditionally comprises the step of disconnecting the trigger signal asthe last step, the loading torque being determined when the triggersignal is disconnected and delivered to the model as long as the speedcalculated by the model is greater than zero and the loading torqueassumes the value zero when the calculated speed is zero.
 9. Methodaccording to claim 8, wherein an induced voltage is delivered as asupply voltage to the model when the trigger signal is disconnected. 10.Method according to claim 9, wherein an integrator for calculating speedand travel is reset at the beginning of the calculation at each risingedge of the trigger signal.
 11. Method according to claim 10, whereinthe method additionally comprises the step of converting the speed intorevolutions per second.
 12. Computer device comprising: a computermemory device that stores program codes for executing the followingsteps for establishing the position of an actuating unit operated by anelectric motor: determining a motor speed from a motor model that takesaccount of afterrunnning of the electric motor and includes speedproportional damping of the motor; and determining the travel completedby the actuating unit by integrating the motor speed over a period oftime and multiplying it by a proportionality factor.
 13. Actuatingdevice, comprising: an electric motor, an actuating unit, which isoperated by the electric motor, a memory unit, a processor, and a memoryunit that comprises program codes for executing the following steps forestablishing the position of the actuating unit operated by the electricmotor: determining a motor speed from a motor model that takes accountof afterrunnning of the electric motor and includes speed proportionaldamping of the motor, and determining a travel completed by theactuating unit by integrating the motor speed over a period of time andmultiplying it by a proportionality factor.
 14. Actuating devicecomprising: an electric motor, an actuating unit, which is operated bythe electric motor, said actuating unit being operable to actuate abrake, a memory unit, a processor, and a memory unit that comprisesprogram codes for executing the following steps for establishing theposition of the actuating unit operated by the electric motor:determining a motor speed from a motor model that takes account ofafterrunnning of the electric motor, and determining a travel completedby the actuating unit by integrating the motor speed over a period oftime and multiplying it by a proportionality factor.
 15. Actuatingdevice comprising: an electric motor, an actuating unit, which isoperated by the electric motor, said actuating unit being operable toactuate a pump device, a memory unit, a processor, and a memory unitthat comprises program codes for executing the following steps forestablishing the position of the actuating unit operated by the electricmotor: determining a motor speed from a motor model that takes accountof afterrunnning of the electric motor, and determining a travelcompleted by the actuating unit by integrating the motor speed over aperiod of time and multiplying it by a proportionality factor. 16.Actuating device comprising: an electric motor, an actuating unit, whichis operated by the electric motor, said actuating unit being operable toactuate a transmission, a memory unit, a processor, and a memory unitthat comprises program codes for executing the following steps forestablishing the position of the actuating unit operated by the electricmotor: determining a motor speed from a motor model that takes accountof afterrunnning of the electric motor, and determining a travelcompleted by the actuating unit by integrating the motor speed over aperiod of time and multiplying it by a proportionality factor. 17.Method for establishing a position of an actuating unit which isoperated by an electric motor, comprising the steps: determining a motorspeed from a motor model that takes account of afterrunnning of theelectric motor by delivering an induced voltage as a supply voltage tothe motor model at the instant of switch off; integrating the motorspeed over a period of time; and establishing the position of theactuating unit by multiplying the result of the integration by aproportionality factor.
 18. Actuating device, comprising: an electricmotor, an actuating unit, which is operated by the electric motor, amemory unit, a processor, and a memory unit that comprises program codesfor executing the following steps for establishing the position of theactuating unit operated by the electric motor: determining a motor speedfrom a motor model that takes account of afterrunnning of the electricmotor by delivering an induced voltage as a supply voltage to the motormodel at the instant of switch off, and determining a travel completedby the actuating unit by integrating the motor speed over a period oftime and multiplying it by a proportionality factor.